Pulse generators which have a movable pattern of periodically repeating regions of different optical density or transparency and an optical sensor in the form of an opto-electrical transducer for detecting that pattern as the pulse generating plate is moved and producing an electrical output in the form of a pulse train can also be known as encoders and can output a certain number of pulses per rotation or a certain number of pulses for a given linear displacement. Such encoders can provide inputs to electronic circuitry for calculating and displaying a position of a rotary member or of a linearly displaceable member.
The pulse generating plate will usually have a given periodicity of the repeating regions of different optical density or transparency and the sensor may be a light curtain, photocell or the like capable of detecting reflected light from the pattern on the movable plate or transmitted light traversing the plate to output the electrical signals which can be for example a succession of high and low voltages. The electrical signal or a component thereof, for example its frequency, amplitude or number of rising or falling flanks represents a measurement of the speed of the moving plate or the extent of movement and optionally the direction of movement.
Such pulse generators or encoders can be used in many machines, for example as rotary encoders, to provide a certain number of pulses per revolution of a machine part at its electrical output. The encoder can be used to signal the speed of the machine part or a motor to enable electronic control, for example, of the motor or of the position of the machine part. Commercially such pulse generators generally have a fixed number of pulses per revolution and in the metric system can provide 1000 pulses per revolution or 5000 pulses per revolution, etc.
Especially simple pulse generators of this type are used in computer mouses. Higher precision pulse generators, especially linear pulse generators are widely used in office printers and especially in ink jet printing machines.
Upon incorporation of such pulse generators in a drive with a fixed output per revolution of the pulse generator may require electronic circuitry to convert the pulse output to the requirements of, for example, a printing machine which may use 300 dots per inch, 600 dots per inch or the like which may not be fully compatible with the metric pulse number per revolution or unit of linear movement described above.
Where there are already pulse generators which deviate from the metric units and allow a resolution in terms of dots per inch, they are relatively expensive to make. The circuitry for conversion usually requires operations such as multiplication and division, generally in a multiplicity of cycles and that can cause deviations in the result of several percent. Problems are encountered when it is not possible to carry out correction with an algorithm which can be practiced with available electronic circuitry.
In the printing field especially, print resolutions are usually given in terms of dots per inch and hence inch measurements are required for positioning the printing head so that optimum and distortion-free printing results can be obtained in each printing pass and direction. When pulse generators of the type described at the outset have been used in the past, the print resolution has been less than satisfactory, distortion and optically visible problems, especially with multicolor printing have arisen.